1. Field of the Invention
The invention relates to a sheet conveying apparatus which conveys a sheet within a sheet conveying path.
2. Description of the Related Art
In the related art, an image forming apparatus of an electrophotographic system, such as a printer, a copying machine, or a facsimile is configured so as to form an image on double sides of a sheet by forming the image one side of the sheet with an image forming portion, reversing the sheet with a reverse portion, and conveying once again the reversed sheet to the image forming portion.
In such an apparatus, a switching member, in which a flapper-shaped member is swingingly configured, is provided to make a switching such that the sheet is conveyed to a discharge conveying path, which discharges the sheet into the outside of the apparatus, or a reverse conveying path, which is provided with the reverse portion. A solenoid is used as a switching unit which switches the switching member to receive instruction from a controller within an image forming apparatus body, and thus the conveying path is selectively switched.
Generally, when a preceding sheet is conveyed to the discharge conveying path side and a succeeding sheet is conveyed to the reverse conveying path side, after a trailing end of the preceding sheet passes through the switching member, the switching member starts a switching operation of the conveying path as the solenoid operates by receiving the instruction from the controller. Then, the switching operation of the conveying path is completed while a leading end of the succeeding sheet reaches the switching member.
However, a speeding-up of the image forming apparatus has been advanced in recent years, and the speeding-up is achieved by shortening an interval between sheets to be conveyed continuously. Meanwhile, the conventional switching operation of the switching member has a certain amount of variation due to a response delay of the solenoid. When the interval between the sheets to be conveyed continuously is gradually shortened, there is a possibility that the interval is not in time between the start and completion of the operation of the switching member due to the variation. In the worst case, the leading end of the succeeding sheet reaches the switching member before the switching operation of the switching member is completed, and thus a jam may occur or the sheet may be damaged.
In order to solve these problems, a following configuration is disclosed in Japanese Patent Laid-Open No. 2001-106409. That is, the solenoid is in ON before the trailing end of the preceding sheet passes through a double-side switching member, and a semi-closed position state is provided to convey while interposing the preceding sheet with the double-side switching member and a conveying guide. Then, when the trailing end of the preceding sheet passes through the double-side switching member, the double-side switching member of the semi-closed position state becomes a completely-closed position.
Thereby, even when the interval between the sheets is short, a conveying path switching operation can be performed. Further, a slip does not occur in such a manner that a conveying force of a reverse roller which reverses the preceding sheet at a downstream side of the double-side switching member is sufficiently larger than a conveying resistance due to an abutting pressure between the double-side switching member and the conveying guide.
In addition, a configuration, which switches the switching member to select three conveying paths, has been proposed Japanese Patent Laid-Open No. 5-286627.
As described above, in Japanese Patent Laid-Open No. 2001-106409, even when the sheet is interposed between the switching member and the conveying member, the slip does not occur in such a manner that the conveying force of the conveying roller which conveys at the downstream side is sufficiently larger than the conveying resistance due to the abutting pressure between the switching member and the conveying guide. However, as the conveying force increases, a size of a motor becomes larger, resulting in increasing the cost. In addition, a roller having a small conveying force, for example, a roller that conveys without a nip, such as a comb-tooth discharge roller is not disposed just behind the switching member.
In addition, due to high image quality in recent years, when the sheet is interposed with the switching member and the guide at a state in which the sheet temperature immediately after fixing is high and a fixed image surface and a conveying rib come in contact with each other, there is a conspicuous problem in that unevenness density of the image between a contact surface and a non-contact surface with the conveying rib is caused.
In addition, since the configuration disclosed in Japanese Patent Laid-Open No. 5-286627 is complicated, a space is required and a manufacturing cost is expensive.